/*
 *  Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */

#include "aligned_malloc.h"

#include <stdlib.h>  // for free, malloc
#include <string.h>  // for memcpy

#include "checks.h"

#ifdef _WIN32

#include <windows.h>

#else
#include <stdint.h>
#endif

// Reference on memory alignment:
// http://stackoverflow.com/questions/227897/solve-the-memory-alignment-in-c-interview-question-that-stumped-me
namespace webrtc {

    uintptr_t GetRightAlign(uintptr_t start_pos, size_t alignment) {
        // The pointer should be aligned with |alignment| bytes. The - 1 guarantees
        // that it is aligned towards the closest higher (right) address.
        return (start_pos + alignment - 1) & ~(alignment - 1);
    }

// Alignment must be an integer power of two.
    bool ValidAlignment(size_t alignment) {
        if (!alignment) {
            return false;
        }
        return (alignment & (alignment - 1)) == 0;
    }

    void *GetRightAlign(const void *pointer, size_t alignment) {
        if (!pointer) {
            return NULL;
        }
        if (!ValidAlignment(alignment)) {
            return NULL;
        }
        uintptr_t start_pos = reinterpret_cast<uintptr_t>(pointer);
        return reinterpret_cast<void *>(GetRightAlign(start_pos, alignment));
    }

    void *AlignedMalloc(size_t size, size_t alignment) {
        if (size == 0) {
            return NULL;
        }
        if (!ValidAlignment(alignment)) {
            return NULL;
        }

        // The memory is aligned towards the lowest address that so only
        // alignment - 1 bytes needs to be allocated.
        // A pointer to the start of the memory must be stored so that it can be
        // retreived for deletion, ergo the sizeof(uintptr_t).
        void *memory_pointer = malloc(size + sizeof(uintptr_t) + alignment - 1);
        RTC_CHECK(memory_pointer);
        if (memory_pointer == NULL)
            return NULL;
        // Aligning after the sizeof(uintptr_t) bytes will leave room for the header
        // in the same memory block.
        uintptr_t align_start_pos = reinterpret_cast<uintptr_t>(memory_pointer);
        align_start_pos += sizeof(uintptr_t);
        uintptr_t aligned_pos = GetRightAlign(align_start_pos, alignment);
        void *aligned_pointer = reinterpret_cast<void *>(aligned_pos);

        // Store the address to the beginning of the memory just before the aligned
        // memory.
        uintptr_t header_pos = aligned_pos - sizeof(uintptr_t);
        void *header_pointer = reinterpret_cast<void *>(header_pos);
        uintptr_t memory_start = reinterpret_cast<uintptr_t>(memory_pointer);
        memcpy(header_pointer, &memory_start, sizeof(uintptr_t));

        return aligned_pointer;
    }

    void AlignedFree(void *mem_block) {
        if (mem_block == NULL) {
            return;
        }
        uintptr_t aligned_pos = reinterpret_cast<uintptr_t>(mem_block);
        uintptr_t header_pos = aligned_pos - sizeof(uintptr_t);

        // Read out the address of the AlignedMemory struct from the header.
        uintptr_t memory_start_pos = *reinterpret_cast<uintptr_t *>(header_pos);
        void *memory_start = reinterpret_cast<void *>(memory_start_pos);
        free(memory_start);
    }

}  // namespace webrtc
